The present invention relates to a film forming apparatus which applies a solution having resin or the like dissolved in it, particularly a resist solution, onto a substrate to be processed, such as a semiconductor wafer, an LC substrate, an exposure mask, or the like.
In the process of manufacturing an LCD or a semiconductor device, for example, photolithography technique is employed to form minute circuit patterns.
In the photolithography technique, resist solution is applied to the surface of a substrate to be processed, such as an LCD substrate, a semiconductor wafer, or the like, thereby forming a film thereon. Thereafter, the film is light-exposed to a specific pattern. Further, the film is subjected to developing and etching, to have a specific circuit pattern.
At present, the spin coating method is most popular as a method of applying resist solution to a substrate to be process and forming a film thereon. In the spin coating method, the resist solution is dripped onto the center part of the substrate, and the substrate is rotated at high speed. The resist solution is thereby spread over the entire surface of the substrate by virtue of centrifugal force. As a result, a resist solution film, which is substantially uniform, can be is formed all over the surface of the substrate.
In recent years, there is the trend that circuit patterns to be formed by photolithography technique have smaller and small wire width. It is therefore strongly demanded that the resist film be made thin. Namely, since the wire width of the circuit to be formed is proportional to the thickness of the resist film and the wavelength of exposure light, it is desirable to make the resist film as thin as is possible.
With the spin coating method it is possible to reduce the thickness of the resist film, by increasing the rotation speed of the substrate. Thus, an 8-inch wafer, for example, is rotated at a considerably high speed of 2000 to 4000 rpm.
The resist applying method, which uses the conventional spin coating method, has the following problems that should be solved.
(1) In the spin coating method, if the substrate to be processed is large, its the circumferential speed is high, causing a turbulent flow of air. The turbulent flow may vary the thickness of the resist film. Due to this, the exposure resolution will be decreased.
The decrease in exposure resolution is a fatal obstruction to an intended increase in the integration density of semiconductor devices. Inevitably, with the conventional spin coating method it is difficult to obtain a uniform resist film having a thickness of 0.4 xcexcm or less. Hence, there is limitation to the manufacture of semiconductor devices of about several gigabytes.
(2) In the spin coating method, the solvent contained in the resist solution gradually evaporates as the resist solution spreads from the center part of the substrate toward the peripheral part thereof. Therefore, the viscosity of the resist solution changes in the direction the solution spreads. Those parts of the resist film, which lie on the center and peripheral parts, respectively, may differ in terms of thickness.
(3) In the spin coating method, the resist solution is wasted in a large amount, spinning off from the peripheral part of the wafer, because the substrate to be processed is rotated at high speed. In one instance, only 10% or less of the resist solution applied onto the wafer contributes to the forming of a resist film.
(4) Further, in the spin coating method, the wafer must be rotated in a cup in order to receive the resist solution spinning off. The resist solution sticking to the cup form particles, which may contaminate the substrate being processed. Hence, it is necessary to wash the cup frequently.
(5) Still further, the spin coating method is disadvantageous in that the resist solution may be applied also to that region of the substrate, such as the peripheral part, which does not contribute to the forming of a circuit. The resist solution applied to this part is usually removed right after the step of applying the resist solution, by a dedicated apparatus called xe2x80x9cedge removerxe2x80x9d.
The present invention has been made in view of the facts mentioned in the paragraphs (1) to (5). Its principal object is to provide a film forming apparatus which can greatly save the solution used to form a film and which can uniformly apply the solution to only the desired part of the substrate that is to processed.
According to the first aspect of this invention, there is provided a film forming apparatus which comprises: a substrate holding section for holding a substrate to be processed; a nozzle unit arranged and opposing the substrate holding section, having a discharge hole for continuously applying film-forming solution, in the form of a slender stream, to a surface of a substrate held by the substrate holding section; and a drive mechanism for driving the substrate and the nozzle unit relative to each other, thereby to coat the surface of the substrate with the solution, while the nozzle unit is applying the solution, in the form of a slender stream, to the surface of the substrate.
With this structure it is possible to apply solution, such as resist solution, in a manner of so-called single-stroke writing. Therefore, the use efficiency of resist solution for forming a film can be much increased. To form a thin film having a uniform thickness, it is necessary to discharge the solution at high pressure in as slender a stream as possible, while moving the nozzle unit at high speed. In this case, it is required that interruption of the solution stream be prevented effectively. To this end, it is desirable to provide an atmosphere control mechanism for maintaining a solvent atmosphere having a predetermined concentration in a space into which the nozzle unit applies the solution.
Here, the atmosphere control mechanism has a main body for accommodating the substrate to be process, a solvent channel provided in the main body for storing solvent controlled in temperature and surface level, and a top plate member provided above the main body and partitioning the space into which the nozzle unit applies the solution. In this case, the top plate member has an insertion section in which the nozzle unit is inserted.
Further, the top plate member may have heating means for heating the nozzle unit and the space into which the nozzle unit applies the solution. If so, the solvent atmosphere can be controlled better, and the viscosity of the solution can be controlled as is desired.
Preferably, the nozzle unit has a solution nozzle for applying the solution in the form of a slender stream, and a solvent nozzle for passing solvent around the solution applied from the solution nozzle.
In this case, the solvent is prevented from evaporating from the solution immediately after the solution is discharged from the nozzle unit, thus effectively the viscosity of the solution from changing. Interruption of the slender stream of the solution can thereby be avoided.
A route-speed setting section may be provided to set a speed at which the nozzle unit and the substrate are moved relative to each other and a route along which the solution is to be applied, in accordance with the amount of solution to apply, the time of applying the solution and the area to coat with the solution. Then, a film of the solution, which is thin and has a uniform thickness, can be formed on the substrate.
Various types of solution application routes can be set. For example, a zigzag route or a spiral route may be set.
To render the thickness of the solution film uniform, it is necessary to maintain the relative speed between the substrate and the nozzle at a constant value. To this end it is desired that a mask member be provided to cover the substrate, except a film-forming region thereof, and that the nozzle unit and the substrate be decelerated, returned and accelerated over the mask member and moved at a constant relative speed over the film-forming region of the substrate.
The mask member may be a plate having an opening that corresponds to the film-forming region. Alternatively, the mask member has a pair of solution receiving members and a drive mechanism for driving the solution-receiving members to control a distance between the solution receiving members.
Further, the solution may be one selected from the group consisting of resist solution, solution for forming an interlayer insulating film, solution for forming a highly conductive film, ferroelectric solution, sliver paste and the like.
According to the second aspect of the present invention, there is provided an apparatus for forming a film on a substrate to be processed, which comprises: a substrate holding section for holding the substrate, with the surface thereof turned downwards; a nozzle unit having a discharge hole for discharging the solution in a form of a slender stream, the discharging hole turned upwards and opposing the substrate held by the substrate holding section; and a drive mechanism for driving the substrate holding section and the nozzle unit relative to each other, thereby to coat the surface of the substrate with the solution, while the nozzle unit is applying the solution, in the form of a slender stream, to the surface of the substrate.
With this structure it is possible to apply solution, such as resist solution, in a manner of so-called single-stroke writing. The use efficiency of resist solution for forming a film can therefore be much increased. Since the substrate is held with that surface turned downwards and the solution is discharged upwards to coat the surface of the substrate, the substrate serves as a cover, effectively preventing solvent from evaporating form the solution, such as resist solution. As a result, Interruption of the slender stream of the solution can be avoided.
Moreover, with this structure, air can be easily expelled since the nozzle unit is arranged with its discharge hole turned upwards.
In the present invention, to form a thin film having a uniform thickness, the solution is discharged at high pressure in as slender a stream as possible, while moving the nozzle unit at high speed. Thus, it is preferred that the discharge hole of the nozzle unit have a diameter of 10 to 200 xcexcm.
It is desirable for this apparatus to further have a reversing mechanism for turning the substrate upside down. The reversing mechanism needs to hold the substrate, without touching that surface of the substrate on which a film will be formed.
Such a slender nozzle as the one used in the present invention has the problem that the discharge hole is easily clogged when it stops discharging resist solution. It is therefore desirable that the nozzle unit have a solvent supplying mechanism for discharge a solvent through the discharge hole of the nozzle unit.
According to the third aspect of the present invention, there is provided a method of forming a film on a surface of a substrate, comprising the steps of: holding a substrate to be processed; and driving the substrate and a nozzle unit relative to each other, while continuously applying film-forming solution, in the form of a slender stream, to the surface of a substrate, thereby to form a film on the substrate.
With this method it is possible to apply solution, such as resist solution, in a manner of so-called single-stroke writing. The use efficiency of resist solution for forming a film can therefore be much increased.
It is desirable that this method have a step of covering the substrate, except the film-forming region, with a mask member.
Preferably, the method further comprises an agitation step of vibrating the substrate coated with the solution, thereby to render flat a surface of a solution film formed on the substrate.
The method may comprise a step of holding the substrate, with the surface, on which a film is to be formed, turned downwards, and the substrate and a nozzle unit may be driven relative to each other, while continuously applying film-forming solution, in the form of a slender stream, to a surface of a substrate, thereby to form a film on the substrate. In this case, the method needs to include a step of turning the substrate upside down to hold the substrate with that surface turned downwards.
It is desired that the method include a step of holding the nozzle unit at a wait position, before a film is formed on the substrate, and that solvent be passed through the discharge hole of the nozzle unit, thereby to prevent clogging in the discharge hole.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.